1. Field of the Invention
The present general inventive concept relates generally to a multibeam laser apparatus and an image forming device using the same. More particularly, the present general inventive concept relates to a multibeam laser apparatus in which a common electrode is used and a dopant density of an isolating unit and varying depths of grooves are formed according to a distance from the common electrode and an image forming device to use the same.
2. Description of the Related Art
Generally, in a printer, a printing speed is decreased as resolution is increased. Accordingly, to improve the printing speed, there is a need for a high resolution printer which may use a short wavelength light source to produce a multibeam laser.
A short wavelength nitride laser apparatus, as a light source of laser printer, can produce a dot size smaller and a depth of focus better than those of a conventional infrared (IR) or red diode laser apparatus.
A multibeam nitride laser apparatus produces a multibeam laser by using an insulator substrate of sapphire (Al2O3) or the like, or a conductive substrate of GaN or the like.
In general, in the case of using the insulator substrate, a laser apparatus is configured, so that an N-type GaN layer, an N-type AlGaN clad layer, an N-type GaN optical waveguide layer, a multi-quantum well (MQW) active layer, a P-type InGaN intermediate layer, a P-type AlGaN cap layer, a P-type GaN optical waveguide layer, a P-type AlGaN clad layer and a P-type GaN contact layer are layered in sequence, and P-electrodes on the P-type GaN contact layer are connected with N-electrodes of an exposed portion of the N-type GaN layer.
Conversely, in the case of using the conductive substrate, a laser apparatus is configured, so that N-electrodes are formed on a lower end of the substrate.
Accordingly, if the multibeam is produced using the insulator substrate, the P-electrodes and the N-electrodes are located on an upper end surface of the same substrate. In this case, it is important to properly connect the inside two P-electrodes to outside electrode pads and to properly connect the N-electrodes.
FIGS. 1 through 3 are views illustrating constructions of conventional multibeam nitride laser apparatuses, respectively.
Referring to FIG. 1, a conventional multibeam nitride laser apparatus is configured in a structure such that four N-electrodes 11, 12, 13, and 14 and four P-electrodes 15, 16, 17 and 18 are formed to control four channels, respectively. The four channels are referred to as Nos. 1, 2, 3 and 4 from the left. To electrically isolate the channel Nos. 1-2 (channel No. 1: arrow in FIG. 1 from 13 to 15; channel No. 2: arrow in FIG. 1 from 11 to 16) and the channel Nos. 3-4 (channel No. 3: arrow in FIG. 1 from 12 to 17; channel No. 4: arrow in FIG. 1 from 14 to 18) from each other, respectively, insulating layers 19 and 20 are additionally formed on the N-type GaN layer in channel No. 1 and channel No. 4, as illustrated. Thus, an electric current flows along a path represented by the arrows illustrated in FIG. 1.
Referring to FIG. 2, another conventional multibeam nitride laser apparatus is configured in a structure such that two N-electrodes 21 and 22 are formed at both sides of four P-electrodes 24, 25, 26 and 27 to allow the left N-electrode 21 to control channel Nos. 1-2 (channel No. 1: from the bottom of 21 toward 24; channel No. 2: from the bottom of 21 toward 25) and to allow the right N-electrode 22 to control channel Nos. 3-4 (channel No. 3: from the bottom of 22 towards 26; channel No. 4: from the bottom of 22 towards 27). That is, each of the N-electrodes controls two P-electrodes. To connect the inside channel Nos. 2 and 3 to the outside N-electrodes 21 and 22, the channel Nos. 2 and 3 and the channel Nos. 1 and 4 are formed with the insulating layer 23 interposed therebetween, as illustrated in FIG. 2.
Referring to FIG. 3, another conventional multibeam nitride laser apparatus is configured in a structure such that a first N-electrode 31 is formed between P-electrodes 30 and 32 of channel Nos. 1-2 (channel No. 1: from 31 towards 30; channel No. 2: from 31 towards 32) and a second N-electrode 34 is formed between P-electrodes 33 and 35 of channel Nos. 3-4 (channel No. 3: from 34 towards 33; channel No. 4: from 34 towards 35) to allow each of the first and the second N-electrodes to control the two P-electrodes. In this case, a path length of electric current is shorter than that of the multibeam nitride laser apparatus of FIG. 1.
The conventional multibeam nitride laser apparatuses as described above have some disadvantages as follows.
In case of the multibeam nitride laser apparatus of FIG. 1, since there is no N-electrode between the respective channels, it can reduce distances between adjacent laser diodes. However, the multibeam nitride laser apparatus requires an additional process, which forms the two N-type GaN layers and selectively forms the insulating layers (19 and 20) therebetween. Also, since the four N-electrodes corresponding to the respective channels are formed, wires for controlling them are increased in number.
In case of the multibeam nitride laser apparatus of FIG. 2, the insulating layer 23, which electrically isolates channel No. 1 from channel No. 2 or electrically isolates channel No. 3 from channel No. 4, is formed having the same height at the respective channels. Accordingly, crosstalk may occur between channel Nos. 1 and 2 and between channel Nos. 3 and 4, respectively.
In case of the multibeam nitride laser apparatus of FIG. 3, the N-electrodes are formed in common between channel Nos. 1 and 2 and between channel Nos. 3 and 4, respectively. Accordingly, distances between the channels become narrowed. As a result, a problem may occur, in that it is difficult to form the laser diode structure having such channels.